Document FR-A-2 542 695 describes a variable-pitch multi-blade rotor of this type, comprising:
a central shaft rotated about a central axis;
a hub constrained to rotate with the central shaft about said central axis;
blades distributed around said central axis and each connected to said central shaft by a twistable element;
a pitch control disk for said blades, said disk being constrained to rotate with said central shaft but being free to slide axially relative thereto; and
means for controlling the sliding of said pitch control disk along said central shaft.
In that known multi-blade rotor, each blade is provided with a cylindrical blade root mounted in bearings provided in said hub and engaged by the pitch-control disk. The cylindrical blade root is made, for example, of light alloy and its bearing surfaces that engage the bearings must receive hard coatings, e.g. of chromium oxide. Furthermore, since the blade itself is generally made of a composite material, e.g. based on carbon fibers, it is necessary to provide a conical flare at one end of said blade serving to secure it in said blade root. As a result the cost of such a known multi-blade rotor is high.
An object of the present invention is to remedy that drawback and to provide a variable-pitch multi-blade rotor of reduced cost and of reduced mass, including a small number of parts, such that it becomes economically feasible to use such a rotor on a light helicopter.